The invention relates to a method for controlling a digital hydraulic controller. Such a controller comprises a set of on/off-valves which are connected in parallel to extend between an input line and an output line of a controller. Usually, each of these valves is connected to one of these lines with a throttle or choke arranged between the line and the valve. In the digital hydraulics technology, the throttle values within one set of valves are set such that the individual flows through the respective valve-line connections form a binary row, e.g. when the smallest flow through the smallest throttle is 1, then the further valve-line connections exhibit a flow rate of 2, 4, 8, 16 etc. Typically, for pressure control, the controller has two sets of valves in which one set of valves connects an input or feed line to an output line of the controller, while the other set of valves connects the output line to a drain line.
By suitably switching suitable combinations of the individual on/off-valves in the controller, flow of fluid through the controller from input line to output line is controlled for controlling either fluid flow or fluid pressure at the output line of that controller. In this way the controller digitalizes the analog behavior of a control edge of a spool valve, so as to replace the latter.
Selection of the suitable valve combinations and the individual opening times and other parameters of operation of the digital hydraulic controller, requires calibration values for each valve and its throttle. When applied to hydraulic cylinder, for example, it has been known to run the cylinder from end to end while observing the linear sensor for the cylinder movement and pressure sensors for the pressures in the individual pressure chambers of the cylinder. From these measurement data, calibration values for the flow or throughput for each valve and its throttle is calculated manually.
However, when the controller is used in practical applications, changes of the temperatures of the working fluid, foreign matter in the working fluid and/or fouling in the valve or throttle may significantly affect the precision of the calibration values spontaneously or gradually. In such cases, the controller becomes inaccurate. Also, improper valve function due to e.g. defects in the solenoid drive may occur which also affect control accuracy.